Analyses of (1,3;1,4) Glucan synthesis during barley coleoptile growth

The cell wall is one of the features that distinguish the structure of plant cells. It contains layers of polysaccharides that affect the development of the cell. (1,3;1,4)-b-Glucan, otherwise known as mixed linkage β-glucan, is a non-cellulosic β-linked polysaccharide and is found primarily in grain cereals. The solubility of these high molecular weight glucan molecules in water is due to the introduction of β-1,3- linkages into the long glucan chain, which causes kinks in the structure and reduces or even eliminates inter-chain hydrogen bonding. Mixed linkage β-glucan's solubility and gel formation are influenced by the uneven distribution of β-1,3-linkages. Although the oligosaccharide pattern varies from a degree of polymerization of DP2-9, generally over 90% of the structure is comprised of blocks of 2 to 3 consecutive b-1,4-linked glucosyl residues separated by single b-1,3-linkages. It has been known for some time that cellulose synthase-like CslF enzymes are responsible for the formation of (1,3;1,4)-b-Glucan, but the mechanisms for how the fine structure is arranged is as yet uncharacterized. In this study we attempted to further elucidate this process through a combination of transcriptomics and cell wall analyses.

Coleoptiles are an ideal tissue in which to study cell wall formation due to their lack of photosynthesis. In this study we extracted mRNA from barley coleoptiles from days 1 to 8 which encompasses the complete functional span of these structures. We performed Illumina NGS and analyzed the data, looking initially at the barley CslF genes. According to the analysis results, while HvCslF transcript level is high in the first four days of coleoptile development, their levels decreased from the 4th day until the 8th day. Especially on the 8th day, it dropped to the lowest levels. We will present data on expression timing and levels of the various HvCslF genes, and show important coexpressing genes. These results are then compared to analyses of the cell wall composition of barley coleoptile cell walls. Additionally, according to our NGS results, lichenase ((1,3;1,4)-b-glucan hydrolase) was found to be highly negatively correlated, expressing at high levels towards the end of coleoptile development. This suggests that it breaks down and recycles b- glucan during the later days of coleoptile growt

Audience Takeaway:
 

Overall, this study contributes to the broader understanding of plant cell wall biology and provides insights that could be leveraged for both fundamental research and practical applications in agriculture and biotechnology.